Method for heating unfinished tellurium-containing steel articles before hot rolling

ABSTRACT

Heating tellurium-containing steel billets, before hot rolling, by moving the billets along a path in a furnace having an oxidizing atmosphere. Providing and maintaining a gas blanket around the billets to protect them from surface oxidation along the hotter portions of the path. Combusting the blanket gas at a cooler portion of the path before the gas is exhausted from the furnace.

United States Patent 1 Hentz et al.

[54] METHOD FOR HEATING UNFINISHED TELLURIUM-CONTAINING STEEL ARTICLESBEFORE HOT ROLLING [75] Inventors: Ronald D. llentz, Crown Point, lnd.;

Gary W. llenger, Homewood, Ill.

[73] Assignee: Inland Steel Company, Chicago, Ill. 22 Filed: nec.2,1910

[21] Appl. No.: 94,282

[52] US. Cl. ..72/38, 72/364, 72/700 [51] Int. Cl. .132") 9/00, 821d31/00 [58] Field of Search ..72/38, 200, 202, 342, 364, 72/365, 700;263/6, 52

[.56] References Cited .UNITED STATES PATENTS l l 1966 Schrader et al...72/364 1 Jan. 16, 1973 3,345,846 10/1967 Hess ..72/364 3,365,922l/l968 Conces'et a1... ..72/38 3,399,873 9/ I968 Dybal et a]. ..263/63,382,700 '5/1968 Heitmann et al.. .....72/364 3,503,240 3/1970 Lawler..72/ 364 Primary Examiner-Charles W. Lanham Assistant Examiner-E. M.Combs Attorney-Merriam, Marshall, Shapiro & Klose 57 ABSTRACT Heatingtellurium-containing steel billets, before hot rolling, by moving thebillets along a path in a furnace having an oxidizing atmosphere.Providing and maintaining a gas blanket around the billets to protectthem from surface oxidation along the hotter portions of the path.Combusting the blanket gas at a cooler portion of the path before thegas is exhausted from the furnace.

9 Claims, 1 Drawing Figure METHOD FOR HEATING UNFINISHEDTELLURIUM-CONTAINING STEEL ARTICLES BEFORE HOT ROLLING BACKGROUND OF THEINVENTION The present invention relates generally to methods for heatingunfinished tellurium containing steel articles, such as billets, priorto hot rolling, and more particularly to a method for heating thesearticles in a manner which deters surface tearing of the articles duringhot rolling. As used herein, the term unfinished steel article includesnot only billets, but also other intennediate steel shapes such asblooms.

The addition of tellurium to steel enhances the machinability of thesteel, but steel containing tellurium undergoes a surface defect knownas surface tearing, during hot rolling of the steel. Surface tearing ismanifest by small cracks on the surface of the article undergoing hotrolling. These cracks occur during hot rolling and are concentrated atthe corners of bars having polygonal cross sections and at sharplocations in ovals being hot rolled into rounds. Surface tearing rendersthe finished article commercially unacceptable.

Surface tearing is to be distinguished from other types of surfacedefects, such as those manifest by cracks in the unfinished steelarticle as it exits from the reheating furnace, before hot rolling.

Prior to the hot rolling of unfinished steel articles into finishedarticles such as rounds, hexagons, or other polygonal shapes, theunfinished articles are subjected to a reheating operation, whichtypically comprises moving the billets through an elongated furnaceheated by burners. Surface tearing is influenced by this reheatingoperation which conventionally occurs in a furnace having an oxidizinginterior atmosphere. An oxidizing atmosphere is generally desirable froma fuel efficiency standpoint, but an oxidizing atmosphere oxidizes asurface layer on the article, and this results in complications whichcontribute to surface tearing of telluriumcontaining steels.

The problem of surface tearing in tellurium-containing steels haspreviously been noted, and attempts to combat surface tearing includereheating the steel article without flame impingement on the surface ofthe article (U.S. Pat. No. 3,287,954, Schrader et al.), reducing themoisture content in the atmosphere of the reheating furnace (U.S. Pat.No. 3,365,922, Conces et al.) and removing the surface and firstsub-layer of the unfinished article, e.g., by scarfing, after reheating(U.S. Pat. No. 3,382,700, Heitmann et al.).

Typical examples of tellurium-containing steel are disclosed in theabove-noted U.S. patents and in Holowaty U.S. Pat. Nos. 3,152,889 and3,152,890.

SUMMARY OF THE INVENTION Surface tearing during hot rolling, and surfaceoxidation or scaling during heating prior to hot rolling, are deterredby a method in accordance with the present invention.

The unfinished, tellurium-containing steel articles move along a path inan elongated reheating furnace extending from a relatively cool furnaceentry to a relatively hot furnace exit. The steel articles are heatedduring this movement with several longitudinally spaced flames eachoriginating at a respective burner located above the path.

A continuous blanket of gas (e.g., natural gas) is provided around thearticles undergoing heating in the furnace, to protect the surface ofthe articles from oxidation. This blanket extends from the furnace exittoward the furnace entry. At least one of the article-heating flamesoriginates near the furnace exit. The gas in the blanket is introducedinto the furnace, also near the exit, beneath the flame there. The gasin the blanket moves upstream from the furnace exit toward the entrywithout substantial mixing of the blanket gas with other gas enteringthe furnace at the burner where the flame originates.

In the furnace, combusted gases are removed from the furnace at anexhaust opening located upstream of the exit; and the blanket gas isburned, in the furnace, before the blanket gas is exhausted. Burning ofthe blanket gas is conducted at a location in the furnace where thetemperature is relatively low, compared to the temperature at thefurnace exit, and where surface oxidation or scaling of thetellurium-containing steel article is not a significant problem.

The blanketgas is combusted by introducing oxygen into the furnace at alocation between the exhaust opening of the furnace and the furnace exit(where the blanket gas is introduced). The furnace is provided with aflame originating at a burner located between the exhaust opening andthe location where the oxygen is introduced, to assure combustion of theblanket gas before it is exhausted. This prevents flame in the exhaustconduit leading from the furnace, as would take place if the blanket gaswere not combusted before it left the furnace.

Other features and advantages are inherent in the method claimed anddisclosed or will become apparent to those skilled in the art from thefollowing detailed description in conjunction with the accompanyingdiagrammatic drawing.

DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic view illustrating afurnace DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG.1, there is illustrated generally, at 10, an elongated furnace in whichtellurium-containing steel billets 11 are heated prior to hot rolling.Billets 11 are moved along a furnace path 12 extending from a furnaceentry 13 to an exit 14.

The billets are heated, as they move along path 12, by flamesoriginating at a number of burners longitudinally spaced along path l2.One flame l5 originates at a burner 25 located at the exit end 30 offurnace l0 and disposed above billets 11 on path 12. Also located abovepath 12 are flames l6, l7 originating at respective burners 26, 27; andlocated below path 12 is flame l8 originating at burner 28. Thedirection and length of the flames are controlled so that they do notimpinge upon the surface of billets ll.

The flames are generated by the combustion of conventional fuel (e.g.,natural gas) and oxygen (using either commercially pure oxygen or air),and com-- busted gases are exhausted through an exhaust opening 20, inthe top of furnace 10, between entry 13 and the burner 27, in thisparticular embodiment the burner located closest to entry 13. Gasesexhausted through exhaust opening 20 are carried away through an exhaustconduit 21.

The atmosphere within furnace is generally slightly oxidizing. Forexample the fuel to oxygen ratio, on a stoichiometric basis, isgenerally about 0.95. This is desirable to assure combustion, in thefurnace, of the maximum amount of combustible fuel. If all the fuel werenot combusted within the furnace (e.g., some fuel being combusted inexhaust conduit 21) less than the full heating potential of the fuelwould be realized in the furnace.

Although an oxidizing atmosphere in the furnace is desirable from a fuelefficiency standpoint, it contributes to the problem of surface tearingof telluriumcontaining steel billets during subsequent hot rolling.

In accordance with the present invention, a continuous blanket of gas isprovided around billets 11, to protect the surface thereof fromoxidation. The gas in this blanket is introduced into the furnace atnozzle 22; and the blanket extends from furnace exit end 30 toward entry13. In this particular embodiment, the blanket terminates just beforethat part of path 12 under flame 17.

The blanket gas is typically natural gas, such as methane, althoughhigher hydrocarbons such as butane, tetrane, ethane and pentane may beused. Carbon monoxide is permissible but not as desirable as thehydrocarbons. Hydrogen should not be used because it is too explosive.

There is a movement of all gases, in furnace 10, from exit end 30 towardexhaust port 20. This movement is essentially horizontal from exit end30 to about wall 31 mounting burner 27. In addition, the blanket gas,injected at nozzle 22, is at a location below the elevation of burners25, 26, 27 where the combustion gases (fuel and oxygen) are introduced.These two factors prevent mixing of the oxygen from the burners with theblanket gas, thereby preventing the blanket gas from being burned offand maintaining the blanket for a substantial distance upstream of exitend 30. The blanket gas introduced at nozzle 22 does not rise to anysubstantial extent to intermingle with the gases introduced at burners25-27 or nozzle 23 until the blanket gas is well upstream along path 12,adjacent burner 27 where the blanket gas is combusted with oxygenintroduced at a nozzle 23, to be described subsequently.

The temperature of furnace 10 is hottest at exit end 30 and thetemperature decreases gradually upstream along path 12 toward entry 13.For example, the furnace temperature at exit end 30 is typically in therange 2,2002,500F. and the billet temperature is typically in the range2,l002,300F. At a location along path 12 just below burner 27, thefurnace temperature is in the range l,8002,000F., and the billettemperature is in the range l,600-l ,700F.

The billets are subjected to maximum surface oxidation in the hottestparts of the furnace. As the furnace temperature decreases, there is areduction in surface oxidation and its resultant adverse contribution tosurface tearing during subsequent hot rolling. Therefore, it isimportant that the blanket of gas be maintained around billets 11 in thehottest part of the furnace, with the importance of blanket maintenancedecreasing as the furnace temperature decreases.

The blanket gas is exhausted through exhaust opening 20 just as are thecombusted gases resulting from the combustion of fuel and oxygenintroduced at burners 25-28. Because of the heat in exhaust conduit 21,especially that portion adjacent exhaust opening 20, any unburnedblanket gas exiting through exhaust opening 20 would combine with anyexcess oxygen or air exiting through exhaust opening 20 and would beburned in conduit 21, causing flames therein. This is undesirable, and,in accordance with the present invention, the blanket gas is combustedin furnace 10 before exiting through exhaust opening 20.

Combustion of the blanket gas is accomplished by introducing oxygen, atnozzle 23 located above path 12 between exit end 30 and exhaust opening20. The oxygen from nozzle 23 is injected downwardly toward and mixeswith the gas blanketing billets 11. Because flame 17 is located betweenoxygen injection nozzle 23 and exhaust opening 20, flame l7 assuressubstantially complete combustion of the blanket gas and the oxygenbefore they reach exhaust opening 20. By preventing uncombusted blanketgases from passing through exhaust opening 20, the likelihood ofcombustion occurring in exhaust conduit 20 is reduced.

Because surface oxidation of the tellurium-containing steel billetsincreases progressively as the temperature rises, it is desirable toburn off the blanket as far back in the furnace, i.e., as close to entry13, as is possible. The closer to entry 13, the lower the temperature.Because the combustion of the blanket gas occurs at a location (adjacentburner 17) along billet path 12 where both the furnace temperature l,8002,000F.) and the billet temperature (l,600l,700F.) are relativelylow, the danger of surface oxidation where the blanket gas is combustedin minimal.

In a typical embodiment, the blanket gas is composed of 98 percentmethane and about 2 percent higher hydrocarbons, such as ethane. Theblanket gas is introduced at a rate in the range 40-80 cubic feet perminute. At burners 15-18, the fuel is introduced at a rate of 2,000cubic feet per minute and the air at a rate of 20,000 cubic feet perminute, a volume ratio of air to fuel of 10 to 1. Oxygen introduced atnozzle 23 is introduced at a rate of about 500 cubic feet per minute.

Typical dimensions for furnace 10 are 45 feet wide and 100 feet long.The vertical dimension between path 12 and furnace roof 19 vary from 3feet high at the low point 32 of the roof and 12 feet high at the highpoint 33 of the roof.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. A method for processing unfinished tellurium-containing steelarticles so as to deter surface tearing during hot rolling, said methodcomprising the steps of:

moving said articles downstream along a path, in a furnace, extendingfrom a relatively cool entry to a relatively hot exit;

heating said articles, as they move along said path,

with a flame originating above said path and without impinging saidflame on said articles; providing a continuous, non-oxidizing blanket ofcombustible gas around said articles undergoing heating, to protect thesurface thereof from oxidation, said blanket extending from said exittoward said entry;

and removing the heated articles from said furnace and hot rolling them.

2. A method as recited in claim 1 wherein:

said flame originates adjacent the exit of the furnace;

and the gas in said blanket moves upstream from said exit toward saidentry end without substantial mixing of said blanket gas with other gasentering said furnace where said flame originates.

3. A method as recited in claim 1 and comprising:

moving the gas in said blanket upstream toward said entry;

exhausting combusted gases from said furnace at an exhaust openinglocated upstream of said exit;

and burning said blanket gas in said furnace before the blanket gas isexhausted.

4. A method as recited in claim 3 wherein:

said burning is conducted at a location in the furnace where thetemperature is relatively low compared to the temperature at said exitand where surface oxidation of the billets is not a significant problem.

5. A method as recited in claim 1 and comprising:

moving the gas in said blanket upstream toward said entry;

exhausting gases from said furnace at an exhaust opening locatedupstream of said exit;

introducing oxygen into the furnace at a location between the exhaustopening and the exit;

and combusting said oxygen with said blanket gas before they areexhausted.

6. A method as recited in claim 5 wherein said last- 10 recited stepcomprises:

' 8. A method as recited in claim 7 and comprising:

providing said furnace with a flame originating adjacent said exit andextending upstream therefrom;

the gas for the blanket being introduced into said furnace at a locationbelow said flame.

9. A method as recited in claim 1 wherein said combustible gas is ahydrocarbon.

2. A method as recited in claim 1 wherein: said flame originatesadjacent the exit of the furnace; and the gas in said blanket movesupstream from said exit toward said entry end without substantial mixingof said blanket gas with other gas entering said furnace where saidflame originates.
 3. A method as recited in claim 1 and comprising:moving the gas in said blanket upstream toward said entry; exhaustingcombusted gases from said furnace at an exhaust opening located upstreamof said exit; and burning said blanket gas in said furnace before theblanket gas is exhausted.
 4. A method as recited in claim 3 wherein:said burning is conducted at a location in the furnace where thetemperature is relatively low compared to the temperature at said exitand where surface oxidation of the billets is not a significant problem.5. A method as recited in claim 1 and comprising: moving the gas in saidblanket upstream toward said entry; exhausting gases from said furnaceat an exhaust opening located upstream of said exit; introducing oxygeninto the furnace at a location between the exhaust opening and the exit;and combusting said oxygen with said blanket gas before they areexhausted.
 6. A method as recited in claim 5 wherein said last-recitedstep comprises: providing said furnace with a flame originating betweenthe exhaust opening and the location where said oxygen is introduced. 7.A method as recited iN claim 1 and comprising: introducing said gas forsaid blanket into the furnace adjacent the exit thereof.
 8. A method asrecited in claim 7 and comprising: providing said furnace with a flameoriginating adjacent said exit and extending upstream therefrom; the gasfor the blanket being introduced into said furnace at a location belowsaid flame.
 9. A method as recited in claim 1 wherein said combustiblegas is a hydrocarbon.